基于特定裸露晶面钒酸铵超薄纳米片的可控合成及储锂机制研究

In view of the inferior cycling life for vanadates, NH4V3O8, a novel high-capacity cathode with relatively stable structure has been proposed in our group. Based on our previous work, herein, the effect of factors in hydrothermal method, such as solution pH values and reaction duration will be investigated in details and the formation regulation of the nanoflake-morphology will be explored. NH4V3O8 nanoflakes with different exposed facets will be synthesized via the certain absorption of various surfactants. The preferable exposed facets with higher electrochemical performance will be optimized and its reaction mechanism will be studied in this project. The as-prepared NH4V3O8 are expected to be further exfoliated into nanosheets with several nanometers in thickness by a high-intensity ultrasonic field. The structure and electrochemical performance of NH4V3O8 nanosheets before and after the treatment will be well compared and the probable exfoliation mechanism will be given. Meanwhile, the behavior of NH4+ group in crystal will be investigated by means of XRD, TG, XPS et al. The kinetics of electrode process and the structural variations during the lithium insertion/extraction process will be studied. For confirming the possibility of intramolecular hydrogen bond, the crystal structure will be deeply analyzed on the basis of structure model in combination with NMR results. Finally,the high-capacity lithium storage mechanism of NH4V3O8 nanosheets will be summarized. Ultra-thin NH4V3O8 nanosheets with long cycling life and high rate capability will be obtained and the strategies for stabilizing the layered structure in this project will greatly contribute to the development of vanadium-based compounds as intercalated materials.

基于钒酸盐普遍存在循环性能较差的问题，我们发展了一种新型结构更稳定的高容量钒酸铵电极材料。在已有工作基础上，本项目拟详细考察水热合成中溶液pH值和反应时间等因素影响，探索片状纳米形貌的形成规律；通过不同类型表面活性剂的特征吸附，可控合成具有不同裸露晶面的目标材料，研究裸露晶面与性能之间的关系，获取钒酸铵的最佳裸露晶面并研究相关反应机理；进一步对片状钒酸铵进行超声剥离以制备超薄纳米片，对比分析剥离前后材料结构和性能的变化，揭示超声剥离的制备机理；采用XRD、TG、XPS等手段深入研究NH4+在充放电过程中的行为；研究钒酸铵的电极动力学过程，考察其在锂离子脱嵌过程中的物相变化规律；深入剖析材料的晶体结构，结合核磁等手段，验证分子内氢键的存在可能，总结材料的高容量储锂机制。通过层间结构稳定化机制的探索，本项目有望获得长寿命和高倍率的超薄钒酸铵嵌锂材料，并丰富相关理论基础。

本项目系统考察了水热合成钒酸铵过程中溶液pH 值和反应时间等因素影响，探索片状纳米形貌的形成规律；研究了片状钒酸铵材料的裸露晶面，并分析裸露晶面与性能之间的关系；采用超声剥离法制备了超薄的钒酸铵纳米片，对比研究了不同溶剂体系对剥离的影响，研究发现材料性能并没有得到显著提高。通过PVP辅助的水热法制备了(NH4)2V3O8纳米片，首次研究了该材料的储锂性能，在150mA/g下首次放电比容量为261.4mAh/g，30次循环后容量保持在215.8 mAh/g。首次将 (NH4)0.5V2O5纳米薄片作为一种新型的水系锂离子电池负极，该材料显示了优异的循环稳定性能，在30mA/g下，前200周循环的容量保持率接近100%。提出了一种以V2O5和硫酸铵为原料制备钒酸铵纳米片的新方法，该材料在60mA/g下，可逆放电容量保持在320mAh/g，。在300mA/g下前60周循环保持率约100%。同时以制备的钒酸铵纳米片为前驱体，通过锂化与钠化，分别得到了钒酸锂和钒酸钠纳米片，深入研究了这些材料在钠离子电池正极与水系锂离子电池负极中的应用。通过Al2O3的表面修饰以及Ar/H2环境下的还原调控，先后制备了类核壳式结构的Al2O3/LiV2O5/LiV3O8和LiV2O5/LiV3O8，相关材料的储锂性能与循环稳定性能均得到了显著提高，对相关材料的储锂储钠机制都进行了深入的研究。在钒系材料之外，我们先后制备了多种新型能源材料如LiTi2(PO4)3, MnO2-CeO2, MnCo2O4 等用于储锂储钠和电催化领域，这些工作对项目是很好的延伸，丰富了研究体系并取得了良好的学术成果。